(1) Field of the Invention
The present invention relates to the plugging of tapholes in furnaces such as, for example, blast furnaces employed in the production of steel. More specifically, this invention is directed to an improved apparatus for use in the sealing of the pouring holes of a shaft furnace and particularly a furnace which operates with a high counter-pressure. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in sealing the pouring holes of a shaft furnace. Such taphole plugging or sealing devices, because of the nature of the viscous material which is injected into the taphole for the purposes of closing the same, are known in the art as "clay guns" or "mud guns". For a general discussion of the operation of clay guns, reference may be had to U.S. Pat. No. 3,765,663 which is assigned to the assignee of the present invention. Reference may also be had to pending application Ser. No. 702,120, filed July 2, 1976 and entitled "IMPROVED CLAY GUN"; the pending application also being assigned to the assignee of the present invention.
The tapholes of modern shaft furnaces are plugged by injecting thereinto, at a very high pressure which is required as a consequence of the high counter-pressure within the furnaces, a sealing compound which generally consists of clay. Because of the requisite high pressure, the clay injecting mechanism or clay gun is coupled to a hydraulic jack which actuates an ejector piston within the clay gun. The clay ejector piston of the clay gun slides within a clay chamber and forces material, previously supplied to this chamber, through a "nose" which is inserted into the furnace pouring hole.
An ejector piston for a clay gun must be carefully designed and constructed taking into account the high operating pressures to which it will be subjected and the abrasive nature of the "clay" which must be moved thereby. A particularly stringent design requirement is that leakage of "clay" past the piston must, to the extent possible, be prevented in the interest of avoiding marring of the surface of the actuator piston rod. The harsh operating conditions, particularly the considerable strains imposed on the ejector piston of a clay gun, and the design requirements for this mechanism dictate that the ejector piston must be either replaced or repaired at regular intervals.
In accordance with previous clay gun designs, access to the ejector piston is possible only after the clay gun has been disassembled from the hydraulic actuator jack and the entire clay chamber dismantled. This is time consuming and thus, from the standpoint of both equipment down time and labor, an expensive procedure.
The operating environment, including the safety considerations incident to the plugging of a furnace taphole, requires that a clay gun be a highly reliable and rugged piece of equipment. Reliability and durability are, particularly considering the difficult working conditions, inconsistent with complexity. It is thus highly desirable, if not mandatory, that the ejector piston of a clay gun be operated to either of its limits of motion as determined by the hydraulic jack actuator, i.e., it is undesirable that there be any intermediate stop positions for the piston of the hydraulic jack actuator. In the prior art, in those cases where the nose portion of the clay gun barrel was removable for servicing, extension of the piston out of the thus opened barrel end could be accomplished only through provision of a complex control system wherein the normal full forward position of the ejector piston correspond to an intermediate stop position of the actuator. Thus, in order to move the ejector piston to a position more advanced than the forward termination of its normal stroke, a sophisticated control for the hydraulic system and a greater length for the hydraulic cylinder would be required. Both of these added requirements would increase the manufacturing cost of the clay gun, inherently increase its complexity and increase the size of a tool for which there is but limited installation space available.
In addition to the periodic repair or replacement of the clay gun ejector piston, it is to be noted that there is customarily a daily maintenance schedule wherein encrusted clay is removed from the cylinder or barrel forward of the ejector piston. It has been proposed to facilitate this daily maintenance by pivotally attaching the ejection nozzle to the clay gun barrel. An example of such a pivotally attached nozzle may be found in U.S. Pat. No. 1,889,433. A loose; i.e., a conventional pivot type connection; is only adequate if the movement of the clay ejector piston terminates short of the joint of the pivot connection. In view of the forces generated, any "play" between the elements to either side of the joint will result in axial or angular relative movement with the resultant creation of a rim on which the piston would hang up.